Endocrinol Metab > Volume 23(2); 2008 > Article
Journal of Korean Endocrine Society 2008;23(2):123-128.
DOI: https://doi.org/10.3803/jkes.2008.23.2.123    Published online April 1, 2008.
Association between Cigarette Smoking and Thyroid Function in Adults without Previous History of Thyroid Disease.
Bo Hyun Kim, Won Bae Kim, Tae Yong Kim, Hong Kyu Kim, Seong Hoon Jeon, Chang Won Lee, Young Kee Shong
1Department of Internal Medicine, Busan St. Mary's Medical Center, Korea.
2Department of Internal Medicine, Asan Medical Center, University of Ulsan College of Medicine, Korea.
3Health Promotion Center, Asan Medical Center, University of Ulsan College of Medicine, Korea.
Abstract
BACKGROUND
Cigarette smoking has a significant impact on thyroid function. However, the association between smoking and thyroid function is incompletely understood. METHODS: We conducted a cross-sectional study that included 90,970 adults (age range: 20 to 79) who had visited the health promotion center at Asan Medical Center between January 1, 2001, and December 31, 2003. Those subjects with previous known thyroid disease, a history of thyroid operation, a history of thyroid function altering medication (herb, estrogen or digestive) or a family history of thyroid disease were excluded. Finally, 47,577 subjects (males: 30,726, females: 16,851) were included in this study. We calculated the age-adjusted geometric mean of the serum TSH and the age-adjusted mean of the serum free T4 among the current, former and never smokers. We also analyzed the age-adjusted prevalence of hypothyroidism and hyperthyroidism among each group. RESULTS: Among men, the geometric mean TSH level was significantly low in the current (1.40 mIU/L, 95% confidence interval [CI]: 1.38-1.41) and former smokers (1.59 mIU/L, 95% CI: 1.57-1.61) compared with the never smokers (1.65 mIU/L, 95% CI: 1.63-1.68). The mean free T4 level was high in the current smokers (1.236 ng/dL, 95% CI: 1.234-1.239) compared with the never smokers (1.234 ng/dL, 95% CI: 1.230-1.238). Similarly, among women, the geometric mean TSH level was low in the current smokers (1.75 mIU/L, 95% CI: 1.67-1.87) compared with the never smokers (1.85 mIU/L, 95% CI: 1.83-1.87). The mean free T4 level was high in the current smokers (1.149 ng/dL, 95% CI: 1.139-1.159) compared with the never smokers (1.138 ng/dL, 95% CI: 1.135-1.140). Among the current male smokers, heavy daily smoking (over 2 packs per day) was more associated with low TSH levels than moderate smoking (less than 1 pack per day). In men, the prevalence of subclinical hypothyroidism was low in the current smokers compared with the never smokers (odds ratio: 0.53, 95% CI: 0.43-0.66). CONCLUSION: We found that current smokers had lower TSH levels and higher free T4 levels than never smokers in both men and women and smoking was associated with a low prevalence of subclinical hypothyroidism in men, which may be of importance when evaluating subjects with subclinical hypothyroidism in Korea.
Key Words: hyperthyroidism, hypothyroidism, prevalence, smoking, thyrotropin


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